Multi-layer fuel and vapor tube

ABSTRACT

A layered tubing for use in a motor vehicle composed of a thick outer tubing having an inner and an outer face, the outer tubing made of an extrudable thermoplastic such as a polyamide like Nylon 12; a thin intermediate bonding layer bonded to the inner face of the thick outer layer, the bonding layer composed of an extrudable melt-processible thermoplastic such as poly butylene terepthalate capable of sufficiently permanent laminar adhesion to the polyamide outer tubing; and an inner layer bonded to the intermediate bonding layer, the inner layer composed of an extrudable, melt-processible thermoplastic such as Nylon 12.

I. RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 07/868,754, filedApr. 14, 1992 now U.S. Pat. No. 5,865,218. This application is one of aseries of four applications dispatched for filing in the U.S. Patent andTrademark Office on Jun. 11, 1992 which can be identified by ourreference numbers: AHBC4049; AHBC4050; and AHBC4051, respectively.

II. FIELD OF THE INVENTION

The present invention relates to a hose for use in a motor vehicle. Moreparticularly, the present invention relates to a multi-layer hose whichcan be employed as a fuel line or vapor recovery line in a motorvehicle.

III. BACKGROUND OF THE INVENTION

Single layer fuel lines and vapor return lines of synthetic materialssuch as polyamides have been proposed and employed in the past. Fuellines employing such materials generally have lengths of at leastseveral meters. It is important that the line, once installed, notmaterially change during the length of operation, either by shrinkage orelongation or as a result of the stresses to which the line may besubject during use.

It is also becoming increasingly important that the lines employed beessentially impervious to hydrocarbon emissions due to permeationthrough the tubing. It is anticipated that future Federal and stateregulations will fix the limit for permissible hydrocarbon emissions dueto permeation through such lines. Regulations which will be enacted instates such as California will fix the total passive hydrocarbonemission for a vehicle at 2 g/m² per 24 hour period as calculated byevaporative emission testing methods such as those outlined in Title 13of the California Code of Regulations, section 1976, proposed amendmentof Sep. 26, 1991. To achieve the desired total vehicle emission levels,a hydrocarbon permeation level for the lines equal to or below 0.5 g/m²per 24 hour period would be required.

Finally, it is also imperative that the fuel line employed be imperviousto interaction with corrosive materials present in the fuel such asoxidative agents and surfactants as well as additives such as ethanoland methanol.

Various types of tubing have been proposed to address these concerns. Ingeneral, the most successful of these have been co-extruded multi-layertubing which employ a relatively thick outer layer composed of amaterial resistant to the exterior environment. The innermost layer isthinner and is composed of a material which is chosen for its ability toblock diffusion of materials such as aliphatic hydrocarbons, alcoholsand other materials present in fuel blends, to the outer layer. Thematerials of choice for the inner layer are polyamides such as Nylon 6,Nylon 6.6, Nylon 11, and Nylon 12.

Alcohol and aromatics in the fluid conveyed through the tubing diffusethrough the tubing wall at rates which differ significantly from thealiphatic components of the fluid being conveyed. The resulting changein the composition of the liquid in the tubing can change the solubilitythresholds of the material so as, for example, to be able to crystalizemonomers and oligomers of materials such as Nylon 11 and Nylon 12 intothe liquid. The presence of copper ions, which can be picked up from thefuel pump, accelerates this crystallization. The crystallizedprecipitate can block filters and fuel injectors and collect to limittravel of the fuel-pump or carburetor float as well as building up oncritical control surfaces of the fuel pump.

In U.S. Pat. No. 5,076,329 to Brunnhofer, a five-layer fuel line isproposed which is composed of a thick outer layer formed of Nylon 11 orNylon 12, a thick intermediate layer of Nylon 6, and a thin intermediatebonding layer between and bonded to the intermediate and outer layersformed of a polyethylene or a polypropylene. On the interior of the tubeis an inner layer of Nylon 6 with a thin intermediate solvent-blockinglayer formed of an ethylene-vinyl alcohol copolymer transposed between.The use of Nylon 6 in the inner fluid contacting surface is designed toeliminate at least a portion of the monomer and oligomer dissolutionwhich occurs with Nylon 11 or Nylon 12.

In U.S. Pat. No. 5,038,833 to Brunnhofer, a three-layer fuel line isproposed in which a tube is formed having a co-extruded outer wall ofNylon 11 or Nylon 12, an intermediate alcohol barrier wall formed froman ethylene-vinyl alcohol copolymer, and an inner water-blocking wallformed from a polyamide such as Nylon 11 or Nylon 12. In DE 40 06 870, afuel line is proposed in which an intermediate solvent barrier layer isformed of unmodified Nylon 6.6 either separately or in combination withblends of polyamide elastomers. The internal layer is also composed ofpolyamides; preferably modified or unmodified Nylon 6 while the outerlayer is composed of either Nylon 6 or Nylon 12.

Another tubing designed to be resistant to alcoholic media is disclosedin UK Application Number 2 204 376 A in which a tube is produced whichhas an thick outer layer composed of polyamides such as Nylon 6 or 6.6and/or Nylon 11 or 12 which are co-extruded with an alcohol-resistantpolyolefin, a co-polymer of propylene and maleic acid.

Heretofore it has been extremely difficult to obtain satisfactorylamination characteristics between dissimilar polymer layers. Thus allof the multi-layer tubing proposed previously has employedpolyamide-based materials in most or all of the multiple layers. Whilemany more effective solvent-resistant chemicals exist, their use in thisarea is limited due to limited elongation properties, strength andcompatibility with Nylon 11 and 12. Additionally, the previousdisclosures fail to address or appreciate the phenomenon ofelectrostatic discharge.

Electrostatic discharge can be defined as the release of electric chargebuilt up or derived from the passage of charged particles through amedium or conduit composed of essentially non-conductive materials. Theelectrostatic charge is repeatedly replenished with the passage ofadditional volumes of fuel through a given non-conductive conduit.Discharge repeatedly occurs in the same localized area gradually erodingthe area and leading to eventual rupture. This, in turn, leads to thedanger of fire and explosion of flammable contents of the tubing.

Thus it would be desirable to provide a tubing material which could beemployed in motor vehicles which would be durable and prevent or reducepermeation of organic materials therethrough. It would also be desirableto provide a tubing material which would be essentially nonreactive withcomponents of the liquid being conveyed therein. Finally, it would bedesirable to provide a tubing material which can easily be renderedcapable of preventing the build-up of electrostatic charge either in anoperation simultaneous with the tube formation or in a post-processingstep or which would be capable of safely dissipating any electrostaticcharge induced therein.

SUMMARY OF THE INVENTION

The present invention is a multi-layer tube which can be used on motorvehicles for applications such as in a fuel line or a vapor return orrecovery line. The tube of the present invention is composed of:

a thick flexible outer tubing having an inner and an outer face, theouter tubing consisting essentially of an extrudable melt processiblethermoplastic having an elongation value of at least 150% and an abilityto withstand impacts of at least 2 ft/lbs at temperatures below about−20° C.;

a thin intermediate bonding layer bonded to the inner face of the thickouter tubing, the bonding layer consisting essentially of an extrudablemelt processible thermoplastic resistant to permeation by short-chainhydrocarbons, the bonding layer consisting of a thermoplastic which ischemically dissimilar to the extrudable thermoplastic employed in theouter tubing and is capable of sufficiently permanent laminar adhesionto the inner face of the thick outer tubing; and

an interior layer composed of an extrudable melt processiblethermoplastic which is capable of sufficiently permanent laminaradhesion to the intermediate bonding layer, the thermoplastic materialin the interior layer having an elongation value of at least 150% and anability to withstand impacts of at least 2 ft/lbs below about −20° C.,the inner layer having a thickness less than the thickness of the outertubing.

The tubing of the present invention may also include an optional outerjacket composed of a suitable melt-processible thermoplastic which iseither co-extruded or applied in a separate processing operation. Thethermoplastic material employed in the optional outer jacket may be anysuitable material which adds insulative or cushioning properties to thetubing jacket. The outer tubing jacket may also, optionally, be capableof dissipating electrostatic energy, the electrostatic dissipationcapacity being in a range between about 10⁴ to 10⁹ ohm/cm².

DESCRIPTION OF THE DRAWING

The objects, features and advantages of the present invention willbecome more readily apparent from the following description, referencebeing made to the following drawing in which:

FIG. 1 is a sectional view through a piece of tubing of the presentinvention; and

FIG. 2 is a sectional view through view through a piece of tubing whichincludes the optional jacket surrounding the outer layer of the tubingof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a multi-layer fuel line and vapor tube whichcontains one outer and one inner tubing layer and at least one bondinglayer interposed therebetween. The tubing of the present invention is,preferably, fabricated by co-extruding given thermoplastic materials ina conventional co-extrusion process. The tubing may either beco-extruded to a suitable length or may be co-extruded in continuouslength and cut to fit the given application subsequently. The tubing ofthe present invention may have an outer diameter up to 50 mm. However,in applications such as fuel lines and vapor recovery systems, outerdiameters of up to 2.5 inches are preferred.

The material may have any suitable total wall thickness desired.However, in automotive systems such as those described herein, totalwall thicknesses between 0.5 mm and 2 mm are generally employed withwall thicknesses of approximately 0.8 to 1.5 mm being preferred. Whileit is within the scope of this invention to prepare a tubing materialhaving a plurality of overlaying layers of various thermoplasticmaterials, the tubing of the present invention generally has a maximumof five layers inclusive of the bonding layers. In the preferredembodiment, the tubing material has three or optionally four layersinclusive of the optional outer jacket layer.

The tubing 10 of the present invention is a material which is suitablefor use in motor vehicles and comprises a relatively thick outer layer12 which is essentially non-reactive with the external environment andcan withstand various shocks, vibrational fatigue, and changes intemperature as well as exposure to various corrosive or degradativecompounds to which it would be exposed through the normal course ofoperation of the motor vehicle.

It is anticipated that both the outer tubing layer 12 as well as anyinterior layers bonded thereto would be suitable for use at an outerservice temperature range between about −40° C. and about 150° C., witha range of −20° C. to 120° C. being preferred. The various layers oftubing are integrally laminated to one another and resistant todelamination throughout the lifetime of the multi-layer tubing. Thetubing of the present invention will have a tensile strength of,preferably, no less than 25N per mm² and an elongation value of at least150%. The tubing will have a burst strength at 23° C. and 120° C. of atleast 20 bar. The multi-layer tubing of the present invention issufficiently resistant to the degradative effects of exposure to brakefluid, engine oil and peroxides such as those which may be found in orprovided by chemical reactions occurring in gasoline.

The outer layer 12 may be composed of any melt-processible extrudablethermoplastic material which is resistant to ultra violet degradation,extreme changes in heat, exposure to environmental hazards such as zincchloride, and degradation upon contact with engine oil and brake fluid.In general, the exterior layer is selected from the group consisting of12 carbon block polyamides, 11 carbon block polyamides as well as zincchloride resistant 6 carbon block polyamides, or thermoplasticelastomers. These thermoplastic elastomers are proprietary compositionsand commercially available under tradenames such as SANTOPRENE, atheremoplastic rubber commercially available from Advanced ElastomerSystems of St. Louis, Mo. KRATON, a thermoplastic rubber composed of astryrene-ethylene/butylene-styrene block copolymer commerciallyavailable from Shell Chemical Co of Houston Tex., SARLINK a proprietaryoil resistant thermoplastic commercially available from NovacorChemicals, Leominster, Mass., and VICHEM a proprietry family ofpolyvinyl chloride compounds commercially available from VichemCorporation. These materials which compose the outer layer can bepresent in their unmodified state or can be modified with variousplasticizers, flame retardants and the like in manners which would beknown to one reasonably skilled in the art.

In the preferred embodiment, a polyamide such as Nylon 12 can beeffectively employed. It is anticipated that a thermoplastic such asNylon 12 may be either modified or unmodified. If modified, it isanticipated that the material will contain various plasticizers as arereadily known in the art. In the preferred embodiment, the polyamidewill contain up to 17% by composition weight plasticizer; with amountsbetween about 1% and about 13% being preferred.

The outer layer 12, preferably, has a wall thickness between about 0.5mm and about 1 mm with a preferred range being between about 0.6 mm andabout 0.8 mm. As indicated previously, the material is extruded byconventional co-extrusion methods to any continuous length desired.

The thermoplastic material employed in the inner layer 14 of the presentinvention is a melt-processible extrudable thermoplastic materialresistant to extreme changes in heat and exposure to chemical intervalssuch as are found in engine oil and brake fluid. The thermoplasticmaterial of choice is, preferably, chemically similar in structure andcomposition to the thermoplastic material employed in the thick outerlayer. As used herein, the term “chemically similar material” is definedas a thermoplastic material selected from the group consisting of 12carbon block polyamides, 11 carbon block polyamides as well as zincchloride resistant 6 carbon block polyamides, thermoplastic elastomersand mixtures thereof. The thermoplastic elastomers which cansuccessfully be employed in the tubing of the present invention areproprietary compositions commercially available under tradenames such asSANTOPRENE, KRATON, SARLINK and VICHEM. The thermoplastic materialemployed in the inner layer of the tubing of the present inventioneither may be identical to the material employed in the thick outerlayer or may be a different thermoplastic selected from those listed totake advantage of specific properties of the various thermoplastics. Inthe preferred embodiment, the inner layer 14 is composed of a materialsimilar to or identical to the thick outer layer. In the preferredembodiment, a polyamide such as Nylon 12 can be effectively employed.

The thermoplastic employed in the inner layer 14 may be either modifiedor unmodified. If modified, it is anticipated that the material willcontain various plasticizers as are readily known in the art. In thepreferred embodiment, the polyamide will contain up to 17% bycomposition weight plasticizer; with amounts between about 1% and about13% being preferred.

The inner layer 14 may have a thickness sufficient to supply strengthand chemical resistance properties to the multi-layer tubing.Specifically, the inner layer 14 is of sufficient thickness to impedepermeation of aliphatic and aromatic hydrocarbon molecules and migrationof those molecules through to the thick outer layer. In the presentinvention, the inner layer has a wall thickness less than that of thethick outer layer. In the preferred embodiment, the inner layer has awall thickness between about 10% and 25% that of the outer layer;preferably less than between about 0.05 mm and about 0.4 mm; with a wallthickness between about 0.1 mm and about 0.3 mm being preferred.

In order to accomplish effective lamination of the two thermoplasticmaterials which compose the inner and outer layers, the tubing of thepresent invention also includes at least one intermediate layer 16interposed between the two previously described layers and co-extrudedtherewith which is capable of achieving a suitable homogeneous bondbetween itself and the two respective layers. The intermediate bondinglayer 16 is generally composed of a more elastic material than thatemployed in the inner layer 14.

In the present invention, the interior bonding layer 16 is a chemicallydissimilar, permeation resistant, chemical resistant, fuel resistantthermoplastic material which is melt processible in normal ranges ofextrusion, i.e. about 175° to about 250° C. By the term “chemicallydissimilar” it is meant that the interior bonding layer 16 is anon-polyamide material which is capable of integral adhesion with andbetween the thick outer layer 12 and the inner layer 14 as a result ofco-extrusion.

The intermediate bonding layer 16 is composed of a thermoplasticmaterial which permits the establishment of a homogeneous bond betweenthe inner and outer layers and exhibits properties of resistance topermeation of aliphatic and aromatic materials such as those found infuel. The thermoplastic material employed herein is preferably amelt-processible co-extrudable thermoplastic which may or may notcontain various plasticizers and other modifying agents.

In the preferred embodiment, the thermoplastic material which comprisesthe interior bonding layer 16 is a thermoplastic polyester derived fromethylene glycol selected from the group consisting of polybutyleneterepthalate, polyethylene terepthalate, polyteremethylene terepthalate,and mixtures thereof. The preferred material is polybutyleneterepthalate. Suitable material is commercially available under thetradename 1607 ZE40 from Huls of Dusseldorf, Germany.

The material may, optionally, be modified to exhibit conductive orstatic dissipative characteristics such as those described previously,if desired. Thus, the intermediate bonding layer 16 may, optionally,include sufficient amounts of a conductive media to effect electrostaticdissipation in the range of 10⁴ to 10⁹ ohm/cm². The intermediate bondinglayer may be rendered electrostatically conductive by the inclusion ofcertain conductive material such as those selected from the groupconsisting of elemental carbon, stainless steel, copper, silver, gold,nickel, silicon and mixtures thereof.

The thermoplastic material employed in the interior layer 16 alsoexhibits characteristics which permit resistance to permeation by shortchain aromatic and aliphatic compounds. These permeation resistantcharacteristics synergistically interact with the inner polyamide layersuch that the total permeation resistance is unexpectedly increased whenthe thermoplastic interior layer is bonded to the inner polyamide layer.Thus, the resistance to permeation to short chain aromatic and aliphatichydrocarbons exhibited by the multi-layer material exceeds thepermeation resistance exhibited by individual layers of eitherpolybutylene terepthalate or polyamide of a thickness equal to orgreater than the multi-ply composite of the present invention.

In the preferred embodiment, the inner layer 14 and the bonding layer 16are maintained at the minimum thickness sufficient to prevent permeationof the fuel through the tubing material to the thick outer layer and onthrough to the outer environment. It is preferred that the amount ofhydrocarbon permeation through the tubing of the present invention be nogreater than 0.55/m² in a 24 hour interval. It is anticipated that thethickness of both the inner and intermediate layers can be modified toaccomplish this end. In the preferred embodiment, the inner layer has athickness between about 0.05 mm and about 0.2 mm with a thickness ofabout 0.1 mm to about 0.2 mm being preferred. The intermediate bondinglayer generally has a thickness less than or equal to that of the innerlayer. In general, the intermediate bonding layer has a thicknessbetween about 0.05 mm and about 0.2 mm with a thickness between about0.1 mm and about 0.2 mm being preferred.

The total wall thickness of the tubing of the present invention isgenerally between about 0.5 mm and about 2.0 mm with a wall thicknessbetween about 0.8 and about 1.25 mm being preferred.

The tubing of the present invention may also, optionally include anouter jacket layer 18 which surrounds the outer layer. The outer jacket18 layer may be either co-extruded with the other layers during theextrusion process or may be put on in a subsequent process such ascross-extrusion. The outer jacket may be made of any material chosen forits structural or insulative characteristics and may be of any suitablewall thickness. In the preferred embodiment, the outer jacket may bemade of a thermoplastic material selected from the group consisting ofzinc-chloride resistant Nylon 6, Nylon 11, Nylon 12, polypropylene, andthermoplastic elastomers such as SANTOPRENE, KRATON, VICHEM and SARLINK.If desired, these materials may be modified to include flame retardants,plasticizers and the like.

The outer jacket may, preferably, exhibit conductive characteristics inthat it is capable of dissipation of electrostatic charge in the rangeof 10⁴ to 10⁹ ohm/cm². The material which composes the outer jacket maybe inherently conductive in these ranges or, preferably, includes in itscomposition a conductive media in sufficient quantity to permitelectrostatic dissipation in the range defined. The conductive media maybe any suitable material of a composition and shape capable of effectingthis static dissipation. The conductive material may be selected fromthe group consisting of elemental carbon, stainless steel and highlyconductive metals such as copper, silver, gold, nickel, silicon andmixtures thereof. The term “elemental carbon” as used herein is employedto describe and include materials commonly referred to as “carbonblack”. The carbon black can be present in the form of carbon fibers,powders, spheres, and the like.

The amount of conductive material contained in the outer jacket isgenerally limited by considerations of low temperature durability andresistance to the degradative effects of the gasoline or fuel passingthrough the tubing. In the preferred embodiment, the thermoplasticmaterial contains conductive material in an amount sufficient to effectelectrostatic dissipation. However, the maximum amount employed thereinis preferably less than 5% by volume.

The conductive material can either be blended into the crystallinestructure of the polymer or can be incorporated during polymerization ofmonomers that make up the polymer. Without being bound to any theory, itis believed that carbon-containing materials such as carbon black may besubject to incorporation into the monomer that produces the surroundingthermoplastic material. Material such as stainless steel are more likelyto be blended into the crystalline structure of the polymer.

What is claimed is:
 1. A layered tubing for use in a motor vehicle, thetubing comprising: a thick flexible outer layer having an inner and anouter face, the outer tubing consisting essentially of an extrudablethermoplastic having an elongation value of at least 150% and an abilityto withstand impacts of at least 2 ft/lbs at temperatures below about−20° C.; a thin intermediate bonding layer bonded to the inner face ofthe thick outer layer, the bonding layer consisting essentially of anextrudable melt processible thermoplastic resistant to permeation byshort-chain hydrocarbons, the bonding layer consisting of athermoplastic which is chemically dissimilar to the extrudablethermoplastic employed in the outer tubing and is capable ofsufficiently permanent laminar adhesion to the inner face of the thickouter layer; and an interior layer having a thickness less than thethickness of the outer layer bonded to the intermediate bonding layer,the inner layer consisting of an extrudable, melt-processiblethermoplastic capable of sufficiently permanent laminar adhesion withthe interior layer having an elongation value of at least 150% and anability to withstand impacts of at least 2 ft/lbs at temperatures belowabout −20° C.
 2. The tubing of claim 1 wherein the intermediate bondinglayer has a thickness approximately equivalent to the thickness of theinterior layer.
 3. The tubing of claim 1 wherein the extrudablethermoplastic of the thick outer layer is a melt-processiblethermoplastic selected from the group consisting of Nylon 11, Nylon 12,zinc chloride resistant Nylon 6, Santoprene, Kraton, Vichem, Sarlink andmixtures thereof.
 4. The tubing of claim 1 wherein the thick outer layercomprises: an effective amount of a polyamide selected from the groupconsisting of Nylon 11, Nylon 12, zinc chloride resistant Nylon 6, andmixtures thereof; and between about 1% and about 17% by volume of athermoplastic plasticizer material.
 5. The tubing of claim 4 wherein thethermoplastic material employed in the intermediate bonding layerincludes as a major constituent an extrudable, melt processiblethermoplastic polyester selected from the group consisting ofpolybutylene terepthalate, polyethylene terepthalate, polyteremethyleneterepthalate, and mixtures thereof.
 6. The tubing of claim 4 wherein thethermoplastic material employed in the intermediate bonding layerconsists essentially of polybutylene terepthalate.
 7. The tubing ofclaim 1 wherein the thermoplastic material employed in the intermediatebonding layer exhibits at least some resistance to interaction withshort-chain hydrocarbon molecules present in material conveyed throughthe tubing.
 8. The tubing of claim 1 wherein the extrudablemelt-processible thermoplastic of the interior layer is selected fromthe group consisting of Nylon 11, Nylon 12, zinc chloride, Nylon 6, andmixtures thereof.
 9. The tubing of claim 8 wherein the thick outer layercomprises: an effective amount of a polyamide selected from the groupconsisting of Nylon 11, Nylon 12, Nylon 6, and mixtures thereof; andbetween about 1% and about 17% by volume of a thermoplastic plasticizermaterial.
 10. The tubing of claim 1 further comprising an exteriorjacket overlying the thick outer layer, the exterior jacket composed ofa material consisting essentially of a thermoplastic rubber selectedfrom the group consisting of Nylon 11, Nylon 12, zinc chloride resistantNylon 6, polyether block amides, Santoprene, Kraton, Vichem, Sarlink,and mixtures thereof.
 11. The tubing of claim 10 wherein said outerjacket is capable of dissipating electrostatic energy, the electrostaticdissipation capacity being in a range between about 10⁴ to 10⁹ ohm/cm².12. The tubing of claim 1 wherein the outer jacket contains quantitiesof a conductive material sufficient to provide electrostatic dissipationcapability in a range between about 10⁴ to 10⁹ ohm/cm².
 13. The tubingof claim 12 wherein the conductive material is selected from the groupconsisting of elemental carbon, copper, silver, gold, nickel, silicon,and mixtures thereof.
 14. The tubing of claim 13 wherein the conductivematerial is present in an amount less than about 5% by volume of thepolymeric material.
 15. A layered tubing for use in a motor vehicle, thetubing comprising: a thick outer layer having an inner and an outerface, the outer layer consisting essentially of an extrudable polyamidehaving an elongation value of at least 150% and an ability to withstandimpacts of at least 2 ft/lbs at temperatures below about −20° C.; anintermediate bonding layer having a thickness between about 0.05 mm andabout 0.2 mm bonded to the inner face of the thick outer layer, thebonding layer consisting essentially of an extrudable non-polyamidethermoplastic capable of sufficiently permanent laminar adhesion to thepolyamide outer tubing and exhibiting at least some resistance toshort-chain hydrocarbon molecules conveyed through the tubing; and aninterior layer bonded to the intermediate bonding layer having athickness between about 0.05 mm and about 0.4 mm, the inner layerconsisting essentially of an extrudable, melt processible polyamidecapable of sufficiently permanent laminar adhesion with the interiorlayer selected from the group consisting of Nylon 11, Nylon 12, zincchloride resistant Nylon 6, and mixtures thereof.
 16. The tubing ofclaim 15 wherein the extrudable thermoplastic of the thick outer layeris a polyamide selected from the group consisting of Nylon 11, Nylon 12,zinc chloride resistant Nylon 6, and mixtures thereof.
 17. The tubing ofclaim 16 wherein the extrudable thermoplastic of the intermediatebonding layer is a thermoplastic polyester selected from the groupconsisting of polybutylene terepthalate, polyethylene terepthalate,polymethylene terepthalate, and mixtures thereof.
 18. The tubing ofclaim 16 further comprising an exterior jacket overlying the thick outerlayer, the exterior jacket composed of a material consisting essentiallyof a thermoplastic rubber selected from the group consisting of Nylon11, Nylon 12, zinc chloride resistant Nylon 6, Santoprene, Kraton,Vichem, Sarlink, polypropylene and mixtures thereof.
 19. The tubing ofclaim 18 wherein said outer jacket is capable of dissipatingelectrostatic energy, the electrostatic dissipation capacity being in arange between about 10⁴ to 10⁹ ohm/cm².
 20. The tubing of claim 15wherein the outer tubing comprises: an effective amount of a polyamideselected from the group consisting of Nylon 11, Nylon 12, Nylon 6, andmixtures thereof; and between about 1% and about 17% by volume of athermoplastic plasticizer material.